Method of sterilizing hygienic paper ware



United States Patent 3,310,364 METHUD 0F STERKLIZING HYGIENIC PAPER WARERohertus Cornelia Johannes Maria Rijssenbeek, Nijmegen, Netherlands,assignor to N.V. Papierfabriek Gennep, Gennep, Netherlands, acorporation of the Netherlands No Drawing. Filed May 19, 1965, Ser. No.457,159 Claims priority, application Netherlands, Dec. 6, 1961,

2 Claims. ((:1. 21-2 This application is a continuation-impart of myearlier copending application Ser. No. 242,366 filed Dec. 5, 1962, andnow abandoned.

The present invention relates to a method of sterilizing hygienic paperware, such as bandages, catamenial padding, handkerchiefs, towels,insulating pads, babies napkins, paper waddings, which latter in atextile cover can be used as quilts, and to hygienic paper waresterilized according to said method.

Hygienic paper articles, of the above types, have long been known andare at present being marketed all over the world in an unsterilizedcondition. Paper bandages are particularly very attractive, beingconsiderably cheaper than those of cotton or other textile fibers, andbecause, especially in the form of cellulosic wadding, it has a veryhigh absorption capacity for moisture. Paper material having a highmoisture absorbing capacity, however, especially cellulosic wadding, hasa very poor wet strength.

The latter drawback also occurs with paper babies napkins but has beenobviated by the addition of one or more layers of paper material havinga high wet strength, which is obtained by adding during the wet stage ofthe manufacturing process, preferably in the beater, a formaldehyderesin to the paper pulp, for example, a ureaformaldehyde resin, amelamine formaldehyde resin, o a phenol formaldehyde resin. The additionof 0.54% by weight of such resins to impart a high wet strength to thepaper is generally known. The addition of such a resin also reducesformation of dust.

When added in a water soluble form, e.g. as a water solubleprecondensate in the wet stage of the paper making process, a relativelysmall quantity of resin is needed to impart a good wet strength to thepaper. This is due to the fact, that under these circumstances the resintends to firmly adhere the paper fibres to each other. When however thesame resin is applied to a finished paper material it is not possible toobtain a paper material suitable to be converted into hygienic paperware.

Accordingly the use of paper material to which resins have been addedafter the wet stage of the paper making process in the practice of thepresent invention is not contemplated.

If such resins in a water soluble form have been added to the paperpulp, preferably in the heater and the pulp is then conducted over thepaper making machine, the resin is cured during the heating in the drypart of the paper making machine to form a water insoluble resin. Thoughon leaving the paper machine the resin has become water insoluble thecuring is not complete. During subsequent storage, the curing continuesfor several weeks and then stops. Generally speaking, the resin is curedmore completely when the paper on the paper making machine has beenheated at a higher temperature and for a longer time. In all caseshowever the resins in commercially available paper ware are onlypartially cured.

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Since soft and absorbent paper ware is heated on the paper machine for avery short time (less than one minute) only, the degree of curing of anyresins present in them is relatively low, though sufficient to make theresins water insoluble and to impart wet strength to the paper.

In many cases it is desirable or necessary to sterilize hygienic paperware, and especially paper bandages, be fore use.

It is known that, in general, articles can be sterilized by dry-heating,e.g. at 180 C. This temperature, however, is unallowably high for allpaper ware, and especially for paper bandages.

It is also known that all sorts of articles can be sterilized by heatingwith steam at 140 C. For absorbent paper Ware this is not desirable,since paper material without a resin is apt to deteriorate under theseconditions, and paper material which has been given a high wet strengthby a formaldehyde resin incorporated in it during the wet stage of theprocess will lose this strength due to the resin being affected. Forthis reason, wet sterilization methods for paper material which has toetain a high wet strength are excluded.

There is a third known method of sterilizing, namely, heating in thepresence of a sterilizing gas, e.g. formaldehyde or ethylene oxide,which is separately supplied for the purpose. The sterilization offinished and packed articles by formaldehyde gas is notoriouslyunreliable because of the slow penetration of the said gas, whereassterilization by ethylene oxide is economically disadvantageous.

There is accordingly aneed for a simple, cheap and reliable method fiordry sterilizing hygienic paper ware, for example, by dry-heating attemperatures up to about C.

It has now been found that such hygienic pape ware into at least part ofwhich a formaldehyde resin has been introduced, by adding it to thepaper pulp during the wet stage of the paper making process, can besimply and fully sterilized without impairing the wet strength or theabsorbency by dry-heating such paper ware, at 60-150 C. for at least 30minutes. The term dry-heating as used in this application is to beunderstood as the heating of paper ware whose water-content is nothigher than air-dry. Air-dry paper ware may contain up to 12% by weightof Water. At temperatures below 60 C. no appreciable quantity offormaldehyde is released from the resin, and heating above 150 C. isdetrimental to the paper. Naturally the treatment at lower temperaturesshould be continued for a longer period than at higher temperatures.Moreover, the period of sterilization depends on the nature of theorganisms present and on the degree of sterilization required. In mostcases, a sterilization for 1-2 hours at 100-1 10 C. is sufficient, butalso in many cases a period of 30 minutes is satisfactory.

It is believed, that the sterilizing action is due to the release offormaldehyde during the further condensation of the partially curedresin. These partially cured formaldehyde resins do not contain freeformaldehyde, but they contain many CH OH groups. During further heatingthese may either be split oil as free formaldehyde or they may reactwith other reactive groups in the resin to provide further curing. Thetotal quantity of formaldehyde released depends on many factors, such asthe temperature, the kind of resin starting material and the initialdegree of curing. In all cases how-ever there is enough formaldehydereleased by prolonged heating, e.g. 30 minutes or more, to effectcomplete sterilization.

It has been found, that after sterilization according to the inventionthere usually remain ample CH OH groups in the resin to sterilize thepaper ware again if it should happen to be contaminated after the firstbe used for bandaging wounds, and be fastened in any of the conventionalmethods, for example, with a closure sheet.

Another feature of the invention is the sterilization of sterilization.5 paper waddin-gs of quilts. Such paper waddings may Suitableformaldehyde resins are urea, melamine, and be used in a textile coverwhich has been separately phenol formaldehyde resins or mixturesthereof. Of, sterilized. These waddings can solve the problem of these,the two first-mentioned resins are the most suithospitals, wheresterilization of blankets is required. able. All commercial resins,which are marketed for The conventional woolen blankets, however, arenot imparting a high wet strength to paper, can be used resistant torepeated sterilization, as they will soon shrink without any furthertreatment, and they may be added to such an extent "as to becomeuseless. to the wet paper pulp from which the paper material In theembodiments of the invention the cellulose for the hygienic articles orfor the resin-containing part Wadding may also contain a formaldhyderesin. It is thereof, preferably in the beater. The proportion of truethat this reduces the moisture absorbing capacity resin is mostly 0.54%by weight, and in most cases to some extent but it also preventsformation of dust: preferably 2% by weight of resin, calculated on theInasmuch as cellulose wadding is apt to be affected air-dry paper. bydry-heating above 110 C., paper material containing Suitable Watersoluble resins for imparting wet strength cellulose wadding ispreferably not sterilized above 110 are phenol formaldehyde resinshaving a phenolzform- C. aldehyde ratio of approximately 2:3. For ureaform- If such a laminated product is heated in a furnace, aldehyderesins the corresponding ratios are 1:2 and preferably at 1001l0 C.,vaporous formaldehyde is preferably 1:2.5. For melamine formaldehyderesins released from the formaldhyde resin, which penetrates the ratiois 1:1 and preferably 2:3. The nitrogen conthe whole bandage and killsall germs present. The tent is then roughly Obviously in each case thewet strength of the resin-containing layer is not appremolecular weightof the condensed resin depends on 25 ciably reduce by such treatment.the degree of condensation, which in turn depends on It has been foundthat the development of formaldethe heating conditions in the papermaking machine. hyde upon heating may continue for hours on a stretch,

Awide variety of such resins for imparting wet strength so that aprolonged sterilization is possible. In some are available commercially.All these resins have in cases, e.g. in the case of bandages, it will benecessary common the property that only part of the CH OH for a productthat has been sterilized earlier, to be sterigroups present in theuncured resin react during the parlized again, and this may also beeffected without detial curing on the paper making machine and duringterioration of the wet strength. subsequent stages, so that suflicientCH OH groups After the sterilization the hygienic paper material mayremain available to develop formaldehyde vapour durbe used immediatelyor it may be kept ready for use ing subsequent heating. or marketed as asterilized package. In the two last- Examples of commercially availableresins are: mentioned cases it is advantageous for the material toTrademark Manufactures Type UrecollK BASF Urea Formaldehyde. Ukadan P 6Sehill und Seilaeher. Do.

Beckamin P682- Reichholdt Ohemie Do. Beetle Resin38 Do. Modnrit M 4Oasella Melamine Formaldehyde. Ciba 286 Olba Do. Paper Resin 605American Oyanamid Corp Do.

The degree of polymerization of the resin and the be packaged first in abacteria-impermeable envelope, molecular ratio of the starting materialsfor the conwhich is resistant to the sterilization temperature anddensation are not critical as far as the sterilization is then to besterilized in the envelope. concerned. As a consequence, it is possiblein all in- Examples of suitable envelopes are closed containers stancesto select the resin which imparts the most favorof glass or metal, suchas steel or aluminum or of thermoable properties after thesterilization, e.g. wet strength, plastic materials, such aspolypropylene or nylon bags. softness and absorption capacity, and alsoto observe When using plastics it is of course necessary not toeconomical considerations. exceed the softening point of the plasticduring the dry- The sterilizable paper ware may, for example, consistheating. An excellent bacteria impermeable envelope of one or aplurality of similar layers of paper material, is a paper bag or anyother well closed paper container e.g. cellulose, tissue containingO.54% by weight of or wrapper. formaldehyde TeSiIL h material for PBacteria impermeable envelopes of the above menable Q P p P l If a 'Yhlgh molstul'e tioned kind are well known in the art and need no furtherabsorbing capaclty 1s desired, for example, for bandages, descriptionnapkms or msulatmg R 5-10 layers of 9 As a material forenvelopes, paperhas the advantage, absorbent paper material, such; as cellulose waddmgthat 1t 1s virtually impermeable to bacteria and yet may be laid on thecellulose tissue, and these may, if M t h so desired, be covered withone or two layers of ab- Permea e o gases I IS eanst at the formaldehydesorbent cellulose tissue having a high wet strength due released by dryheatmg can P. through the to a suitable content of formaldehyde resin.Such lamipaper There thus no danger that Sterlllled bandages Hatedbandages may be cut up into Pieces of the may stlll contain traces ofharmful formaldehyde. sired SiZe For a bandage this may, for example, beAs the formaldehyde resins are entirely stable at the 15 X 30 or 30 X 30temperature of the human body, there is no danger that It i l o ibl tWrap a f layers of absorbent a wound treated with a bandage sterilizedin accordance paper material in one or more layers of cellulose tissuewith 0111 invention Will irritated y Subsequently containing aformaldehyde resin. Such a packet may leased formaldehyde. The resinsper se do not irritate the wound, for in the ready product they arebonded to the fibre in the condensed state.

The invention is illustrated by means of the following examples:

Example I A cellulose tissue web was made from a batch of paper pulpconsisting of 40% Boweler bleached sulphate pulp, having a fiber lengthof about 1 mm., made from hardwood and 60% Wezerhainzer bleachedsulphite pulp, having a fiber length of 3-4 mm., made from soft wood.While this pulp was being worked in the beater, there was added to it aquantity of water soluble urea formaldehyde resin sold under thetrademark Urecoll K. This resin has a urea formaldehyde ratio of 1:2.5.

The quantity of resin was chosen so as to yield a cellulose tissue witha resin content of 2% by weight. After thorough mixing the pulp was fedto a paper making machine and used in the customary way to produce acellulose tissue having a weight of 22 g./m. a dry breaking length inmachine direction 850 m. and a wet breaking length of 250 m. During thepassage of the web through the paper making machine the cellulose tissueremained in contact with heated rolls for 1.8 sec. This period wassufficient to cure the water soluble resin to form a partially curedwater insoluble product which firmly bonds the cellulose fiberstogether. The finished cellulose tissue had a soft touch and was able toabsorb 8 times its own weight of water. Entirely similar materials areobtainable from many commercial sources. 30

Example III A packet of 10 layers of cellulose wadding was divided intopieces of x 30 cm. with a thickness of approximately 8 mm. These pieceswere folded into two layers of cellulose tissue containing 2.5% byweight of melamine formaldehyde resin calculated on the air-drymaterial. Thereafter the bandages were sterilized by heating for 1 /2hours at 100-105 C. After cooling no viable micro-organisms could beisolated from the bandages, and the wet strength and themoisture-absorbing capacity had not changed to any appreciable extent.

The cellulose cloth was made in the same way as described in Example I,except that 2.5% of Madurit M4 was added instead of 2% of Urecoll K. Thewet strength of this cellulose cloth was 32% of the dry strength.

Example IV The operations described in Example I were repeated with thedifference that the cellulose tissue contained different kinds ofdifferent resins, as appears from the following table. In this table PhFindicates a phenol formaldehyde resin, UP a urea formaldehyde resin andMF melamine formaldehyde resin. The figure under the heading Ratioindicates the mol ratio of phenol, urea or melamine to formaldehyde. Themolecular weight given is the average molecular weight of the watersoluble resin; the quantity of resin is expressed as percent by weightof partially cured resin in the finished but unsterilized cellulosetissue.

Two sheets of this cellulose tissue were laid upon each other. Uponthese were laid six layers of cellulose wadding. These did not containany resin and had been manufactured from cellulose fibres in a customaryway to yield a web with a weight of 8.5 g./m. and then creped to yield aweb of 17 g./m. Upon these were laid two more sheets of the cellulosetissue and the layered product was cut up into bandages measuring 15 x30 cm. The thickness of the bandages was approximately 5 mm.

A number of these bandages were rolled up, inserted in a glass tubeclosed with a polypropylene stopper, heated for one hour at 104 C. andsubsequently cooled. Upon examination a sample of these bandages wasfound not to contain any viable germs. The breaking length in dry, stateof the cellulose tissue had increased to 910 m. After 30 minutesimmersion in water at room temperature the breaking length was 320 m.The wet strength of the bandages had remained very good and the moistureabsorbing capacity had not changed to any appreciable extent.

Example II From the same packet of 6 layers of cellulose wadding and 4layers of cellulose tissue as in Example I sheets of 100 x 180 cm. werecut, destined as a wadding for sterilizable quilts. The pieces werepackaged in flat condition in a well-closed paper bag made of ordinarywrapping paper and the whole was heated in a furnace for 45 minutes at105 C. The quilt wadding was entirely sterilized, and could be used in aseparately sterilized cover of textile fabric.

The sterilistation was carried out in all cases by heating for 1 hour atC. in a glass test tube, closed with a plug of cotton wool. The bandageswere in each case tested by a standard procedure to show the presence ofany visable, micro-organisms. In all cases complete sterility wasobtained.

I claim:

1. A method of sterilizing hygienic paper ware comprising preparingmoisture absorbent paper material of which at least a part has anenhanced wet strength and includes 0.5-4% by weight based on said partof a partially cured formaldehyde resin distributed therein and adaptedfor enhancing said wet strength of said paper material, said resin beingselected from the group consisting of phenol formaldehyde resins, ureaformaldehyde resins and melamine formaldehyde resins, said resin beingintroduced into the paper pulp during the preparation of the papermaterial and partially cured to form a resin containing a substantialquantity of CH OH groups capable of releasing free formaldehyde onheating, at temperatures from at least about 60 C., enclosing said papermaterial in a bacteria impermeable envelope capable of resisting asterilization temperature to be applied thereto, and dry heating thematerial in said envelope at a temperature within the range of from 60to C. for at least 30 minutes and sufiiciently long to sterilize thepaper material by the action of the formaldehyde vapor which is therebyreleased.

2. A method as claimed in claim 1 comprising dry heating the papermaterial in said envelope at a tempera- 7 8 ture Within the range offrom 100 to 120 C. for at least 2,582,840 1/ 1952 Maxwell 177155 X 30minutes. 2,831,749 4/1958 Marinaro et al. 212 X 2,839,355 6/1958 George2158 References clted y the Examiner 2,999,789 9/1961 Quinn 162 166 XUNITED STATES PATENTS 5 EIG NTS 1,219,451 3/1917 Gardos 16784 X2,029,525 2/1936 Ellis 117 155 50,755 1/1910 swltlerland- 2,297,69810/1942 Freeman 117-155 2,482,525 9/1949 Wachter 117 155 X MORRIS O.WOLK, Primaly Examiner. 2,559,234 7/1951 Steam 117155 10 I. ZATARGA,Assistant Examiner.

1. A METHOD OF STERILIZING HYGIENIC PAPER WARE COMPRISING PREPARINGMOISTURE ABSORBENT PAPER MATERIAL OF WHICH AT LEAST A PART HAS ANENHANCED WET STRENGTH AND INCLUDES 0.5-4% BY WEIGHT BASED ON SAID PARTOF A PARTIALLY CURED FORMALDEHYDE RESIN DISTRIBUTED THEREIN AND ADAPTEDFOR ENHANCING SAID WET STRENGTH OF SAID PAPER MATERIAL, SAID RESIN BEINGSELECTED FROM THE GROUP CONSISTING OF PHENOL FORMALDEHYDE RESINS, UREAFORMALDEHYDE RESINS AND MELAMINE FORMALDEHYDE RESINS, SAID RESIN BEINGINTRODUCED INTO THE PAPER PULP DURING THE PREPARATION OF THE PAPERMATERIAL AND PARTIALLY CURED TO FORM A RESIN CONTAINING A SUBSTANTIALQUANTITY OF -CH2OH GROUPS CAPABLE OF RELEASING FREE FORMALDEHYDE ONHEATING, AT TEMPERATURES FROM AT LEAST ABOUT 60*C., ENCLOSING SAID PAPERMATERIAL IN A BACTERIA IMPERMEABLE ENVELOPE CAPABLE OF RESISTING SSTERILIZATION TEMPERATURE TO BE APPLIED THERETO, AND DRY HEATING THEMATERIAL IN SAID ENVELOPE AT A TEMPERATURE WITHIN THE RANGE OF FROM 60TO 150*C. FOR AT LEAST 30 MINUTES AND SUFFICIENTLY LONG TO STERILIZE THEPAPER MATERIAL BY THE ACTION OF THE FORMALDEHYDE VAPOR WHICH IS THEREBYRELEASED.